The principle of rotary machines with three pistons rotating in an enclosure on a crankshaft was first described years ago, for instance in U.S. Pat. No. 3,349,757 (J. I. M. Artajo), patent application WO 94/16208 (B. Tan). These machines are commonly used as engines or pumps.
These three-piston rotary machines were later adapted to work inside the enclosures of rotary machines with a deformable rhombus (RMDR), whose non-circular external shape can contain a deformable rhombus shaped rotor. Furthermore, rotary machines with a deformable rhombus having four chained pistons present geometric particularities that are well known, and reported in patent FR2936272 (V. Génissieux) or patent application WO8600370 (Contiero) in particular.
The possibility of rotating a rotor with three pistons articulated in their middle on a crankshaft with three arms at 120° inside an enclosure with the profile of a RMDR is known and has been described in patents FR 1404353 (J. Lemaître, et al) and U.S. Pat. No. 3,295,505 (A. Jordan) in particular.
However, these state of the art three-piston rotary machines are limited and inefficient. Indeed, only the external variable volume cavities (cavities formed between the pistons and the enclosure) of the machines are functional, i.e. perform a function on the working fluid corresponding to the primary use of the machine, e.g. intake, compression, exhaust for engine mode use, or aspiration, discharge for use in pump mode. The central volume, i.e. formed below the pistons, is not used, or used as a secondary function of the machine, enabling, for example, a cooling function in U.S. Pat. No. 3,295,505 (A. Jordan) or a lubrication function in other applications.
These three-piston rotary machines are therefore relatively inefficient, particularly when compared with four-piston, deformable rhombus machines.
A machine as described in patents DE 1,451,741 and DE 2,047,732 to G. Finsterhoelzl, whose geometry is incompatible with RMDR type enclosure profiles, has three variable volume cavities or chambers below its pistons, but these three chambers are only used for accessory functions, such as lubrication. The displacement of the three chambers below the piston is small compared with that of the external chambers and cannot intrinsically be increased, and certainly not to equal the displacement of the external variable volume cavities.
In this context, the present invention aims to provide a three-piston rotary machine with better power/size and power/mass ratios than the state of the art three-piston machines, with a factor of improvement of around 2 to 2.5, while also offering an economic advantage over machines with four chained pistons, which have a large number of parts and are more complex to produce.